1. Technical Field
This disclosure generally relates to image forming apparatuses, and particularly to the structure of a waste fluid tank in an image forming apparatus.
2. Description of the Related Art
As an example of image forming apparatuses, which include printers, facsimile machines, copiers, plotters, and multifunction peripherals, an inkjet recording apparatus is known that employs a recording head configured to eject droplets of ink. The recording head ejects the ink droplets via a nozzle onto a recording medium, such as a sheet of paper, in order to form (i.e., record, print, transfer, etc.) an image thereon as the recording medium is transported.
The inkjet recording apparatus comes in two types. One is the serial type in which the recording head is moved in a main scan direction as it ejects ink droplets. The other is the line type in which the recording head does not move when it ejects ink droplets.
The term “recording medium” on which the image is formed is herein intended to refer to not only a sheet of paper but also various media of various materials on which ink droplets can be landed to form a desired image. Thus, the “recording medium” includes sheets of threads, fibers, cloth, fabrics, leather, metals, plastics, glass, wood, and ceramics, for example. To “form an image” is herein intended to refer to not only the imparting of an image with some meaning, such as letters or figures, onto a recording medium but also the imparting of an image without any apparent meaning, such as random patterns, onto the medium (by simply landing ink droplets onto the medium). The term “ink” is intended to refer to not only what is generally called “ink” but also any fluid with which an image can be formed on the recording medium. Such fluid may therefore be referred to as “recording fluid” or “fixing solution”.
The structure of the recording head in an inkjet recording apparatus gives rise to several inherent problems. For example, the ink viscosity increases and the ink may even solidify if a solvent component of the ink evaporates out of the nozzle. An ejection defect or a recording failure may be caused by the accumulation of dust or grime on the nozzle or by the entry of air bubbles into the nozzle. Thus, the inkjet recording apparatus is normally equipped with a maintenance/recovery mechanism for maintaining or recovering the intended performance of the recording head.
For example, the maintain/restore mechanism includes a cap (which may be also referred to as a “capping unit” or a “cap member”). When the apparatus is not being used, the recording head is sealed with the cap in order to prevent the drying or increase in viscosity of the ink within the nozzle. In another example, ink droplets that do not contribute to the recording operation are ejected before, after, and/or during the recording operation, so that the ink with increased viscosity within the nozzle can be ejected in order to recover or maintain the ejection performance of the nozzle.
Such ejection of ink droplets not contributing to image formation but that is performed for maintaining nozzle performance may be referred to as a “preliminary ejection” or “blank ejection”. During the blank ejection, the ink droplets are ejected into a dedicated blank ejection receptacle or the cap.
An example of the waste fluid tank (which may also be referred to as a “waste fluid container”, or a “waste fluid reservoir unit) for collecting the waste ink fluid produced by the recording head maintenance/recovery operation is disclosed in Japanese Laid-Open Patent Application No. 2005-119210. In this example, the waste ink fluid sucked out of the head into the cap and the ink blank ejected into a receptacle are collected in the same waste fluid tank.
Japanese Laid-Open Patent Application No. 2007-253471 discloses another example of the waste fluid tank. The waste fluid tank includes a waste fluid inlet and an atmosphere communicating hole, wherein an absorbing body for absorbing the waste fluid is disposed between the waste fluid inlet and the atmosphere communicating hole. In yet another example disclosed in Japanese Laid-Open Patent Application No. 2003-285452, the waste fluid tank also includes an absorbing body.
Japanese Laid-Open Patent Application No. 2001-162829 discloses yet another example of the waste fluid tank consisting of a fixed waste fluid reservoir unit and a detachable waste fluid reservoir unit. Furthermore, Japanese Laid-Open Patent Application No. 2007-76339 discloses an arrangement for detecting a filled-up state of the waste fluid tank, wherein a fill-up detecting absorbing body is installed on the side of an opening for the entry of waste fluid.
Japanese Laid-Open Patent Application No. 2005-199526 discloses a waste fluid tank of hermetically sealed structure, wherein the inside of the tank is opened to the atmosphere when the waste fluid is introduced into the waste fluid tank.
The aforementioned image forming apparatuses and their waste fluid tanks are disadvantageous in the following respects.
When a waste fluid of a quick-drying ink, such as a pigment-based ink, is collected in a waste fluid tank, the waste fluid increases in viscosity upon contact with air and produces a deposit of ink. The waste fluid may also dry after it is absorbed in the absorption member, thereby blocking the absorption of subsequent waste fluid.
There are the two kinds of waste fluid that is produced as a result of the maintenance/recovery operation. One is the waste fluid that accumulates in the cap into which the ink is ejected by the recording head. The other is the waste ink that collects in the blank ejection receptacle member into which the ink is ejected from the recording head. When the waste fluids from these two sources are collected in the same waste fluid tank, the utilization efficiency of the waste fluid tank decreases as the waste fluids turn into a deposit as mentioned above.
In order to control the drying of the waste fluid, the waste fluid tank may be air-tightly structured. However, in this case, an opening must be provided to the tank in order to release air out of the tank into the atmosphere, for example, so that the waste fluid can be introduced into the waste fluid tank.
When a fill-up detecting unit is installed in an airtight waste fluid tank for detecting the filled-up state, there is the problem that, if the fill-up detecting unit is installed nearer to the waste fluid introducing position than the atmosphere opening, the filled-up state is detected before the waste fluid reaches a level up to which the waste fluid tank should be capable of holding the waste fluid, thus lowering the utilization efficiency of the waste fluid tank.
On the other hand, in the case of a non-airtight waste fluid tank having an opening portion for the entry of waste fluid, the collected waste fluid leaks out of the opening portion when the image forming apparatus and hence the waste fluid tank are tilted.